Reference points and lines used in the panoramic radiographic analysis. UROr indicates the most inferior and lateral point of upper right orbit; ULOr, the most inferior and lateral point of upper left orbit; RFm, the midpoint of right mental foramen; LFm, the midpoint of left mental foramen; UROr-ULOr, line connecting UROr to ULOr; RFm-LFm, line connecting RFm to LFm; 13k;23k;33k;43k, the lines representing the mesiodistal angulations of teeth 13, 23, 33, and 43, respectively; and 16m;26m;36m;46m, the lines representing the mesiodistal angulations of teeth 16, 26, 36, and 46, respectively